1. Field of the Invention
The present invention relates generally to printer cartridges and particularly to a drive shaft-auger arrangement used within a cleaner assembly for moving waste toner within the printer cartridge.
2. Description of the Related Art
Inside each print cartridge, unusable “waste” toner is created as a byproduct of an electro photography (EP) process. All of the toner that is picked up by a photoconductive drum from a developer roll is ideally transferred onto a media sheet or a transfer belt in the case of a two-step toner transfer process. However, due to inefficiencies within the transfer process, all of the toner put on the photoconductive drum by the developer roll does not get transferred to the media sheet or transfer belt. The waste toner left on the photoconductive drum after it has contacted the media sheet or transfer belt must be removed so a clean photoconductive drum can be written to again by a laser. For this reason, a cleaner blade is placed in constant contact with the photoconductive drum to wipe the waste toner from its surface before it is re-charged and imaged again. This cleaner blade prevents the waste toner from a previous photoconductive drum revolution from contaminating the toner developed during the next photoconductive drum revolution. The waste toner removed by the cleaner blade falls into a sealed waste toner compartment disposed beside the photoconductive drum to prevent it from being distributed inside the printer.
The waste toner collected during transfer must be properly stored inside the waste toner compartment. As the photoconductive drum is in contact with the media sheet or transfer belt, there is very little storage space for waste toner around the cleaner blade. Generally, an auger is positioned in a cleaner housing disposed adjacent to the photoconductive drum. Rotational motion of the auger allows the waste toner to be delivered to the waste toner compartment from the photoconductive drum. Augers have proved to be an effective means of moving toner from one area to another for a wide variety of toner applications.
Augers used for transferring waste toner are usually made from either molded plastic or metal wire stock. However, each of these types of augers has its own drawbacks. For example, injection molded plastic augers have proved to be easier to manufacture compared to the metal wire variety. In addition, providing a drive for a plastic auger is more straightforward because the drive shaft for the auger can be molded in the same cavity as the helix, resulting in a simple one piece design. However, the problem with the plastic molded augers is that these are most often resistant to bending and can only transfer waste toner in straight channels. Comparatively, the metal wire augers have an advantage of being able to bend during waste toner transfer and as a result transfer the waste toner through a curved channel thereby effectively.
A barrier for practical implementation of metal wire augers is the need for a metal drive shaft used to connect the auger with its drive source. Having a metal drive shaft on which to fix the auger is advantageous in that the auger can be soldered or welded onto the drive shaft without an attachment part such as a screw, pin or other retainer. However, metal drive shafts add significant cost to the overall auger design, decreasing its likelihood for use in production laser cartridges.
Some manufacturers have used a plastic drive shaft instead of metal drive shaft to reduce some of the above problems faced by the metal drive shafts. For example, the cost of the drive component is reduced substantially by using plastic instead of a machined or cast metal part. Also, an additional processing station such as welding or soldering is not needed if the drive is made from plastic. Finally, a plastic drive shaft makes it easier to attach the gearing that is needed to turn the assembly.
However, securing or coupling the metal auger to the plastic drive shaft is a significant obstacle in designing a plastic drive shaft. The coupling mechanism must fit inside the auger channel without interference in order for the auger to turn freely. Further, the size of the coupling mechanism is also generally very small, making it difficult to transmit the torque needed without risk of breakage. An alternative employment of a coupling mechanism between the auger and the plastic drive shaft is to mold the auger into the plastic drive shaft to form a unitary device. Unfortunately, this method is very sensitive to manufacturing parameters and is a much more expensive alternative to hand assembly.
Thus, there is a need to provide a secure coupling between an auger and corresponding drive shaft that addresses at least some of the above problems and still provide a reliable waste toner removal operation from the photoconductive drum to the waste toner compartment in a printer cartridge.